Thermoplastic resins are commonly combined with fibers, particles, and other solids to make reinforced composites. The solids in the composite can increase tensile strength, dimensional stability, and other physical and mechanical characteristics of the articles made with the composites. For example, glass fibers may be combined with a thermoplastic resin composition to produce a glass fiber-reinforced composite (GFRC) with high tensile strength and improved rigidity. The glass fibers may take various forms, such as continuous or chopped strands, rovings, woven or non-woven fabrics, and continuous or chopped strand mats.
The thermoplastic resin composition and glass fibers may be supplied by a extruder to a compression- or injection-molding machine so that they can be formed into the GFRC. Typically, resin pellets and fiberglass are fed together or separately into the extruder. During the extrusion process using single or twin-screw machines, the resin is melted and the fibers are dispersed throughout the molten thermoplastic resin to form a fiber/resin mixture. Next, the fiber/resin mixture may be degassed, cooled, and formed into pellets. The dry fiber strand/resin dispersion pellets may then be had to a molding machine and formed into molded composite articles that have a substantially homogeneous dispersion of glass fibers throughout the composite article.
One difficulty with combining the thermoplastic resin composition and the fibers is the typically high viscosity of the melted resin composition. In many instances, thermoplastic polymers heated to a melting temperature have a viscosity well above room temperature water, more akin to a carbohydrate syrup such as room temperature molasses. Increasing the temperature of melted thermoplastic resin further can reduce the viscosity, but also increases the risk the resin will thermally decompose.
Thus, there is a need for developing methods of making fiber-reinforced thermoplastic composites that permits a thermoplastic resin composition to be combined with fibers at lower viscosity. There is also a need for methods of reducing the viscosity of the thermoplastic resin composition without heating a polymerized thermoplastic resin to its decomposition temperature. The present application addresses this and other challenges in making reinforced thermoplastic composites.